Well, we have a very nagging problem on the MCE, Live TV, Recorded TV, Music, Radio - all was fine, the only issue was whenever we saw a DVD, even with the MCE and Windows volume all the way to maximum, the sound was not loud enough to hear and quite often we had to switch on the sub-titles just to follow what is going on.
Finally, though it seems I have found a fix - and it seems to be working. I was using the AC3 filter and the DTS/5.1 encoding. In the AC3 Config, you need to change the preset default to an aptly one names Loud, which fixes the issue.